It is notorious that in order to chill the freezing cylinders of ice cream making machines, said cylinders are arranged in heat-exchange relationship with the evaporator of a refrigerating unit. Usually, this is carried out by helically winding the evaporator tubing about the outer surface of the freezing cylinder, and then by welding it or by fixing it With suitable heat-conducting adhesives to said cylinder, so as to promote heat transfer extensively between these two elements. This method is time-consuming and expensive, and it does not achieve an optimum heat transfer. It has been also suggested, as disclosed for instance in the Italian Patent No. 464.025 filed Apr. 19, 1950, to line the freezing cylinder with an outer liner acting as an expansion chamber for the compressed gases coming from the compressor of the refrigerating unit. This system eliminates, due to the direct expansion of gases, the drawbacks connected to the heat-transfer; however, also this system cannot be worked out easily due to the difficulties in welding the outer liner to the surface of the freezing cylinder.
From EP-A-0 395 080 a method for the manufacture of a reactor vessel is known comprising the steps of forming an inner cylindrical sleeve from a single continuous sheet of metal with a single length wise weld, welding a continuous spiral support to the outer wall surface of said inner sleeve, forming an outer cylindrical shell around said sleeve by pressing said inner surface of said shell firmly against said continuous spiral support and forming a single longitudinal weld to form a continuous spiral flow path around said inner sleeve in cooperation with said spiral support.
Also this method is difficult to be worked out, due to the difficulties in welding the spiral support to the inner sleeve, and further due to the difficulties of tightly adhering the cylindrical shell against the said spiral support.